Glazing pigment and method for the production thereof

ABSTRACT

In a method for the manufacture of a nacreous pigment, in which a multilayer film is produced by vacuum evaporation coating on a substrate and, after release from the substrate, the particles thus produced are comminuted to pigment particles of a desired size, vapor deposition of a plurality of layers taking place at separate locations within an evacuable container and the substrate being passed along the sources of evaporation, it is provided that at least a backing (A), in particular a silicon oxide layer, and at least a metal oxide layer (B), in particular a titanium oxide layer, are vapor-deposited on the substrate, in particular a circulating metal belt.

[0001] The invention relates to a nacreous pigment and a method for themanufacture thereof, in which a multilayer film is produced by vacuumevaporation coating on a substrate and, after release from thesubstrate, the particles thus produced are comminuted into pigmentparticles of the desired size, vapor deposition of a plurality of layerstaking place at separate locations within an evacuable container and thesubstrate being passed along the sources of evaporation. Depending onthe layer structure, interference phenomena may occur in pigments of thegeneric type.

[0002] Nacreous pigments are used in lots of fields of application, inparticular for decorative purposes, car paints, cosmetic purposes or inthe field of safety printing.

[0003] In known manufacturing processes, an inorganic salt, for examplesodium chloride, is applied on the surface of the substrate as anintermediate layer that ensures subsequent detachment from thesubstrate, with several layers then being deposited by CVD or PVDcoating and the multiple layered compound, after leaving the vacuumarea, being detached in the form of individual particles by waterdissolution.

[0004] An apparatus for putting into practice a method of the generictype in which a circulating metal belt is employed as a substrate, isknown from German patent application 199 02 141, which is no priorpublication. It specifies, by vapor deposition, to produce a reflectingor substrate layer of aluminum, on which, by subsequent evaporation, todeposit a transparent layer, for instance of magnesium fluoride ortitanium oxide.

[0005] DE 12 42 778 provides that the vapor-deposited layers consist ofthe group of zinc sulfide, zinc oxide, guanine, magnesium fluoride,titanium dioxide, calcium fluoride and cryolite, with a material fromthe group of alkali halides, alkaline earth halides or alkali borates,such as Na₂B₄O₇; B₂O₃; MgCl₂, being used as a substrate for these films.

[0006] Evaporation temperatures depend on the respective chromogenicsubstance or substrate.

[0007] Interference phenomena are employed for chromogenic purposes byexploitation of the path difference of the light waves that isdetermined by reflection on the interfaces produced by the variousdeposited layers. These effects of interference are affected by thethickness of the individual layers and the index of refraction thereof.In the case of an uncolored pearlescent pigment, the product of filmthickness in nm and refractive index is to remain within a range between10 and 200.

[0008] Interference colors are produced when this product is in a rangeabove 200, the brightest colors occurring with a given pigment weightconcentration in the range of 200 to approximately 1500. Color intensityalso depends on the uniformity of platelet thickness i.e., on the planeparallelism of the substrate and the plane parallelism of the depositedlayers, because pigment platelets of irregular thickness reflect varyingcolors which may cancel one another so that there is no color effect orno production of pure colors.

[0009] A summary of the current prior art is to be found in Chem. Rev.1999, 99, pages 1963 to 1981, which illustrates that maximal reflectionshifts to shorter wave lengths as the angle of view grows.Correspondingly, a thin film with incident white light can show colorsthat change along the entire spectrum of visible light from red to blueas a viewer's angle of view becomes flatter. It is also shownmathematically that greater variance of thickness results in lessdefined colors, which is the case for example with natural mica used asa substrate. Correspondingly, individual particles exhibit interferencephenomena, which is not the case with an arrangement of severalparticles. The optical characteristics of such a natural mica basedarrangement are nearly the same as those of an individual metal oxidelayer, in particular a TiO₂ layer. As compared to this, more recentlyused pearlescent luster pigments on the basis of artificially producedaluminum oxide and silicon oxide substrates have a constant thickness,thus becoming part of the optical system. Multilayer oxide coatings onthe basis of SiO₂ substrates exhibit stronger and brighter interferencecolors than is the case with mica as a substrate.

[0010] Liquid-phase or gas-phase precipitation leads to significantporosity, frequently of more than 25 percent of the layer. This porositylessens the intensity of the reflected light.

[0011] As for the production of inorganic films, vacuum evaporationcoating—also using electron beams—sputtering and the CVD method arespecified as methods known per se. However, these methods are mentionedto be rather costly and therefore used only for optical lenses, filtersand the like.

[0012] As for the production of TiO₂ flakes, continuous filmfragmentation is mentioned as a familiar method, the films beingproduced for instance by thermal hydrolysis of TiOCl₂. Alternativesconsist in the deposition of titanium alkoxide on a surface andfragmentation of the resulting film by vapor treatment, in depositingcolloidal TiO₂ solution on a glass surface and scratching off theresulting film. Mention is also made of the application of a TiOCl₂solution on a gelatin film and detachment of the gelatin film, vacuumdeposition, acid treatment of potassium titanate and subsequent heating,or the production and fragmentation of hollow TiO₂ particles from a mixof a surfactant with a colloidal TiO₂ solution. Substrate-free TiO₂flakes may also be obtained by the substrates being dissolved in strongacids or bases.

[0013] In the production of TiO₂ coated mica from a TiOCl₂ solution,attention must be paid to the reactor geometry and the mixingconditions. The TiO₂ layers obtained may be coated with organic dyes aswell as with thin layers of silver, nickel or compositions of variousmetals in order to obtain a darker shade.

[0014] DE-AS 1 136 042 teaches to use substrates of a low refractionindex in the form of oxides or oxide hydrates of metals of the IVthand/or Vth group, for example SiO₂, and to coat them with substances ofa higher refraction index, for example oxides of Ti, Fe, Sb, Sn etc.

[0015] The production of the platelets there described is implemented bya glass, ceramic, metal or plastic substrate being wetted with asolution of a hydrolysable compound of the metal that is to be convertedinto the desired oxide; from the liquid film thus produced, therespective oxide or oxide hydrate is formed as a thin coating bysubsequent heating.

[0016] U.S. Pat. No. 3,438,796 teaches to produce pigment platelets thatconsist of a plurality of films of silicon oxide and aluminum, with thesilicon film serving as a protective layer for the aluminum on the onehand and for producing interference effects in dependence on itsthickness on the other. The aluminum film may be adjusted in thicknessso that it is substantially impermeable to light. The layers areproduced by chargewise vapor deposition.

[0017] EP 0 803 549 provides silicon oxide layers to be vapor-depositedon conventional platelet particles of a length of for instance 1 to 200μm. The platelets must consist of a metallically reflecting material ormetal alloys. Alternatively, the use of mica may be considered. Itfurther specifies that it is a familiar way of proceeding to deposit, onsuch a substrate of a colorless oxide, crystallized titanium oxidelayers, for instance in the form of rutile, on which to deposit anotherlayer of colored inorganic material such as iron oxide.

[0018] Earlier studies have shown that the refraction index andabsorption of vapor-deposited silicon oxide layers are the lower, theslower evaporation takes place and the greater the oxygen content, sothat there is the possibility to manipulate the optical propertiesduring vapor deposition.

[0019] By subsequent treatment or subsequent coating, all the pigmentsdescribed above are stabilized towards weather factors and light.

[0020] Proceeding from this, it is the object of the invention to embodya method for the manufacture of a nacreous pigment and a nacreouspigment that can be manufactured at a high production rate and excels byexcellent durability properties and a wide range of possible colorsaccompanied with high color saturation and opacity.

[0021] According to the invention this object is attained by at leastone backing layer, in particular a silicon oxide backing layer, and atleast one metal oxide layer, in particular a titanium oxide layer beingvapor-deposited on the substrate, in particular a circulating metalbelt.

[0022] The silicon oxide layer thus deposited helps create a backingwhich, after being peeled off the substrate, namely the metal belt,excels by high plane parallelism and defined thickness in particular ascompared to natural mica platelets, but also to platelets produced bywet-processing.

[0023] As opposed to natural mica, the SiO starting material usedaccording to the invention does not have any impurities, for instanceiron. Further, there is no need of complicated preparation such ascalcination, comminution, grading etc.

[0024] Due to its simple way of manufacture, the backing according tothe invention also has advantages over synthetic mica (phlogopite),which has never gained any commercial importance because of complicatedmanufacturing requirements at high pressure and elevated temperature.

[0025] The vapor deposition rate and oxygen partial pressure helpregulate the optical properties such as the refraction index andreflection coefficient of the backing, it being possible in this way toproduce defined and reproducible shades and changes of color independence on the angle of view.

[0026] The thickness of the layer that is vapor-deposited subsequently,in particular a titanium oxide layer, can also be regulated as desiredthrough the vapor deposition rate and/or the metal belt velocity,possessing excellent plane parallelism due to the plane surface of thepreviously deposited silicon oxide layer.

[0027] As opposed to pearlescent pigments coated by wet chemicaldeposition, the pigments produced according to the invention are planeparallel as far as to the outer edge. The result is higher color purityand improved luster even in minor particles, because the scattered-edgeportion is minimized.

[0028] There are no secondary precipitations as they occur in wetchemical processes. Further, there are virtually no crystal germs as abasis for crystal growth, because the substrate has a very low porosityand a smooth surface.

[0029] As a result of the manufacturing method according to theinvention, the pigment platelets peeled off the backing have largelyidentical and reproducible optical properties, for example the sameshade of color when viewed from a certain angle.

[0030] The pigments obtained according to the invention have great shearstability. This is due to the fact that excellent bonding of the SiO andTiO layers is obtained by the method according to the invention. Ascompared to this, the shear stability of natural-mica-based pigments israther bad due to the layered structure thereof and the morphology ofthe metal oxide layer.

[0031] The thickness of both layers is easy to regulate, in particularas compared to the hydrolysis belt method (shrinking of the depositedlayer), and the color can be influenced in this way, with the thicknessof the SiO layer influencing the color even stronger than the thicknessof the TiO layer.

[0032] In the method according to the invention, there is no waste offilm and, correspondingly, no need of costly waste disposal. Accordingto the invention, it is conceivable to use substances that have a highevaporation temperature, such as TiO, which would not be possible inconventional methods that use a plastic film, because of the lack oftemperature resistance of these films.

[0033] In as much as the term layer sequence is mentioned above or inthe following, this implies protection also of the reverse layersequence because, once the platelets are peeled off the substrate, theorientation originally given by the substrate does no longer exist.

[0034] In keeping with the invention, provision can be made for thebacking to be enclosed on both sides by metal oxide layers of varyingthickness (asymmetric layer structure). Of course, such a layerstructure cannot be obtained by wet chemical processes. As the pigments,when they are worked into paint and when an object is painted, will belocated substantially parallel to the painted surface, varying thicknessof the metal oxide layers will result in that, randomly distributed,either the thicker or thinner metal oxide layer is on top, which helpscreate colors and paints of novel interference effects.

[0035] Provision may further be made for another metal layer, inparticular an aluminum layer, to be vapor-deposited on a three-layeredarrangement as described above, it being possible to obtain strongopacity of these pigments by a correspondingly adjusted layer thickness.In a manner known per se, a comparatively thin silicon oxide layer maybe vapor-deposited as a protective layer on the aluminum layer.

[0036] In keeping with another embodiment, it is provided that a metaloxide layer and the backing layer are followed by a metal layer, asilicon oxide layer and another metal oxide layer, the metal layer beingaluminum, chromium, gold, copper, silver or the like.

[0037] In keeping with another embodiment, it is provided that the metaloxide layer and the backing are followed by a metal layer, the metalagain being aluminum, chromium, gold, copper, silver or the like.

[0038] The thickness of the backing preferably ranges between 20 and1000 nm, the thickness of the metal oxide layer preferably rangesbetween 20 and 500 nm and that of the metal layer preferably between 40and 60 nm.

[0039] The above-specified pigments according to the invention may havefurther layers on their surface, for example for increased weatheringresistance. These layers can be applied by wet chemical or PVD processes(“inline”).

[0040] Suitable substances may be selected from the group of oxidesand/or oxyhydrates and/or hydroxides of aluminum, silicon, zirconium,phosphor, boron, zinc, cerium, manganese, chromium, molybdenum, iron andtin. The mentioned stabilizing substances may also be incorporated as adoping agent in the outermost layers.

[0041] In keeping with the method according to the invention, it isprovided that first a backing is produced by vacuum evaporation coatingof a circulating metal belt; and that, after parting from the substrate,the backing particles thus produced are comminuted to a desired size,these backing particles then being equipped with another layer by wetcoating. Use is made in particular of the fundamental advantages,specified above, of backing particles that are precipitated on a metalsubstrate and the subsequent coating can then be put into practice byfamiliar wet coating techniques. The backing may consist in particularof silicon oxide, silicate, boron oxide, borates, aluminum oxide,aluminates, titanium boride or mixtures thereof.

[0042] Provision may further be made for the backing particles tocomprise network formers or network modifiers and/or barium sulfate forsurface smoothing and/or soluble or insoluble inorganic or organiccolorants.

[0043] The layers applied by wet chemical deposition may advantageouslyconsist of oxides of the metals zirconium, chromium, titanium, iron,zinc, oxide hydrates of these metals, ferrotitanates, titanium suboxidesor mixtures thereof, it being possible to reduce the metal oxides. In amanner known per se, additional coatings may be applied for lightstabilization and weathering resistance.

[0044] Another embodiment of the method according to the inventionrelates to the manufacture of single-layer nacreous pigments,wherein—apart from light stabilization and weathering resistancecoatings that might be provided—a single, optically active layer oftitanium oxide, iron oxide, titanium suboxides, titanium oxinitrides,molybdenum sulfide or ferrotitanium oxide is vacuum-deposited on acirculating metal belt. Such single-layer structures preferably have anoptically active layer of a thickness in the order of magnitude of 20 to500 nm, preferably 40 to 100 nm. These single-layer structures excel incolor brightness and purity. Putting them into practice has so farfailed due to lacking shear stability, which can however be obtained bythe process according to the invention.

[0045] Another embodiment of the method according to the inventionrelates to the manufacture of nacreous pigments from a metal oxidelayer, in particular a titanium oxide layer, a metal layer and anothermetal oxide layer, in particular a titanium oxide layer, by vacuumevaporation coating on a circulating metal belt. The metal may bealuminum, chromium, gold, copper, silver or the like.

[0046] In order for the coating to be parted from the substrate moreeasily, a release coat may be applied, consisting of a paint, a salt, asalty compound or an organic material. Precipitation of this releasecoat may for instance take place by painting or evaporation.

[0047] The invention also relates to a nacreous pigment manufactured inaccordance with one of the described methods as well as to paints,lacquers, cosmetics and plastics that comprise these nacreous pigments,and the use of these nacreous pigments for the production of paints,lacquers, cosmetics and plastics.

[0048] Details of the invention will become apparent from the ensuingdescription of exemplary embodiments.

EXAMPLE 1

[0049] A release layer of a water soluble salt that is indecomposablyhigh-vacuum evaporable is applied by vacuum (10⁻⁴ mbar) evaporationcoating on a circulating metal belt, which is followed by a TiO layer,an SiO layer and another TiO layer.

[0050] The belt circulation speed is 2 m/s, the temperature of the TiOsources is 2200° C., the temperature of the SiO source 1450° C. Thedistance of the evaporation sources from each other is 17 cm.

[0051] The optical thickness of the SiO layer is 202 nm, that of the TiOlayers 198 nm.

[0052] After being parted from the metal belt in a water bath, the filmis stirred by a high-speed stirrer and comminuted into pigment particlesof a size of 1 to 100 μm.

[0053] The powder obtained has a blue color.

EXAMPLE 2

[0054] A release layer of a water soluble salt that is indecomposablyhigh-vacuum evaporable is applied by vacuum (10⁻⁴ mbar) evaporationcoating on a circulating metal belt, which is followed by a TiO layer,an aluminum layer and another TiO layer.

[0055] The belt circulation speed is 2 m/s, the temperature of the TiOsources is 2200° C., the temperature of the aluminum source 650° C. Thedistance of the evaporation sources from each other is 17 cm.

[0056] The optical thickness of the aluminum layer is 245 nm, that ofthe TiO layers 603 nm.

[0057] After being parted from the metal belt in a water bath, the filmis stirred by a high-speed stirrer and comminuted into pigment particlesof a size of 1 to 100 μm.

[0058] The powder obtained has a light blue color of metallic characterand nacreous luster.

EXAMPLE 3

[0059] A release layer of a water soluble salt that is indecomposablyhigh-vacuum evaporable is applied by vacuum (10⁻⁴ mbar) evaporationcoating on a circulating metal belt, which is followed by a TiO layer.

[0060] The belt circulation speed is 2 m/s, the temperature of the TiOsources is 2200° C.

[0061] The optical thickness of the TiO layer is 500 nm.

[0062] After being parted from the metal belt in a water bath, the filmis stirred by a high-speed stirrer and comminuted into pigment particlesof a size of 1 to 100 μm.

[0063] The powder obtained has a reddish yellow color.

EXAMPLE 4

[0064] A release layer of a water soluble salt that is indecomposablyhigh-vacuum evaporable is applied by vacuum (10⁻⁴ mbar) evaporationcoating on a circulating metal belt, which is followed by an SiO layer.

[0065] The belt circulation speed is 2 m/s, the temperature of the SiOsource is 1450° C.

[0066] The optical thickness of the SiO layer is 200 nm.

[0067] After being parted from the metal belt in a water bath, the filmis stirred by a high-speed stirrer and comminuted into pigment particlesof a size of 1 to 100 μm.

[0068] Subsequently, the powder obtained is coated in a known mannerwith titanium dioxide by wet chemical treatment.

[0069] Depending on layer thickness, pigments of varying interferencecolors are obtained.

[0070] Measuring the optical layer thicknesses takes place by thequartz-crystal thin film monitoring method.

1. A method for the manufacture of a nacreous pigment, in which amultilayer film is produced by vacuum evaporation coating on a substrateand, after release from the substrate, the particles thus produced arecomminuted into pigment particles of a desired size, vapor deposition ofa plurality of layers taking place at separate locations within anevacuable container and the substrate being passed along the sources ofevaporation, characterized in that at least a backing (A), in particulara silicon oxide layer, and at least a metal oxide layer (B), inparticular a titanium oxide layer, are vapor-deposited on the substrate,in particular a circulating metal belt.
 2. A method according to claim1, characterized in that first a metal oxide layer (B), in particular atitanium oxide layer, is vapor-deposited, then a backing (A), inparticular a silicon oxide layer, and then another metal oxide layer(B′), in particular a titanium oxide layer.
 3. A method according toclaim 2, characterized in that the metal oxide layers (B, B′) havevarying thicknesses.
 4. A method according to claim 1, characterized inthat, on a metal oxide layer (B), in particular a titanium oxide layer,a backing (A), in particular a silicon oxide layer, is vapor-deposited,which is followed by another metal oxide layer (B′), in particular atitanium oxide layer, and an aluminum layer.
 5. A method according toclaim 4, characterized in that a silicon oxide protective layer isvapor-deposited on the aluminum layer.
 6. A method according to claim 1,characterized in that, on a metal oxide layer (B), in particular atitanium oxide layer, a backing (A), in particular a silicon oxidelayer, is vapor-deposited, on which is vapor-deposited a metal layer,then a metal oxide layer, in particular a silicon oxide layer, andanother metal oxide layer, in particular a titanium oxide layer.
 7. Amethod according to claim 6, characterized in that the metal isaluminum, chromium, gold, copper or the like.
 8. A method according toclaim 1, characterized in that, on a metal oxide layer (B), inparticular a titanium oxide layer, a backing (A), in particular asilicon oxide layer, is vapor-deposited, which is followed by a metallayer (C).
 9. A method according to claim 8, characterized in that themetal is aluminum, chromium, gold, copper, silver or the like.
 10. Amethod according to one of claims 1 to 9, characterized in that thethickness of the backing (A) ranges between 20 and 1000 nm.
 11. A methodaccording to one of claims 1 to 10, characterized in that the thicknessof the metal oxide layer (B) ranges between 20 and 500 nm.
 12. A methodfor the manufacture of a nacreous pigment, characterized in that firstthe backing is produced by vacuum evaporation coating of a circulatingmetal belt and, after release from the substrate, the backing particlesthus produced are comminuted to a desired size, these backing particlessubsequently being provided by wet coating with at least another layer.13. A method according to claim 12, characterized in that the backingparticles consist of silicon oxide, silicate, boron oxide, borates,aluminum oxide, aluminates, titanium boride (TiB₂) or mixtures thereof.14. A method according to claim 12, characterized in that the backingparticles comprise network formers or network modifiers and/or bariumsulfate for surface smoothing and/or soluble or insoluble inorganic ororganic colorants.
 15. A method according to claim 12, characterized inthat the layers applied by wet chemical deposition consist of oxides ofthe metals zirconium, chromium, titanium, iron, zinc, oxide hydrates ofthese metals, ferrotitanium, titanium suboxides or mixtures thereof. 16.A method according to claim 15, characterized in that the metal oxidesare reduced.
 17. A method according to claim 12, characterized in thatadditional coatings are applied for light stabilization and weatheringresistance.
 18. A method for the manufacture of a nacreous pigment,characterized in that a single optically active layer consisting oftitanium oxide, iron oxide, titanium suboxides, molybdenum sulfide orferrotitanium oxide is produced by vacuum evaporation coating on acirculating metal belt; and, after release from the substrate, theparticles thus produced are comminuted to a desired size; andsubsequently light stabilization and weathering resistance coatings areapplied by wet chemical deposition.
 19. A method according to claim 18,characterized in that the optically active layer has a thickness in theorder of magnitude ranging from 20 to 500 nm, preferably from 40 to 100nm.
 20. A method according to claim 1, characterized in that a metaloxide layer, in particular a titanium oxide layer, a metal layer andanother metal oxide layer, in particular a titanium oxide layer, arevapor-deposited on a substrate, in particular a circulating metal belt.21. A method according to claim 20, characterized in that the metal isaluminum, chromium, gold, copper, silver or the like.
 22. A nacreouspigment produced in accordance with the method according to one of thepreceding claims 1 to
 21. 23. A paint, lacquer, cosmetic or plasticmaterial comprising a nacreous pigment according to claim
 22. 24. Use ofa nacreous pigment according to claim 22 for the production of paints,lacquers, cosmetics and plastics.